Effect of chemoreceptor stimulation on the periodicity of renal sympathetic nerve activity in anesthetized cats.

The effect of chemoreceptor stimulation, with asphyxia (1 min), hypoxia (2 min) or hypercapnia (2 min), on the periodicity of synchronized renal sympathetic nerve activity (RNA) was examined in anesthetized cats before and after peripheral chemoreceptor and baroreceptor denervation. RNA was filtered between 50-3000 Hz, rectified and integrated. Time intervals, less than 500 ms, between synchronized interburst intervals were measured and used to produce periodicity histograms. Under control normoxia two major periodicities were evident, a Tc rhythm between 6 and 17 c/s comprising 34 +/- 5% (+/- SE) of measured intervals and a Tb rhythm between 2 and 6 c/s with a 66% probability. The mean periods of Tc and Tb were 110 +/- 6 ms and 299 +/- 7 ms respectively. The periodicity distribution and mean Tc and Tb rhythms for RNA discharge under various chemoreceptor stimulations were not significantly changed despite significant increases in arterial blood pressure in all cases. The amplitude and overall number of synchronized RNA peaks were however increased with chemoreceptor stimulation. When asphyxia was applied under a constant arterial pressure the periodicity of synchronized RNA still was not significantly altered. Baroreceptor and peripheral chemoreceptor denervation led to an increase in the probability of the Tc mode and reduction in the Tb mode, once again the application of chemoreceptor stimulation did not significantly alter the frequency distribution of synchronized RNA. The results indicate that chemoreceptor stimulation does not affect the 10 c/s fundamental rhythm and the stability of gate operators altering Tc/Tb proportions, although it can alter the number of active fibres and interacts with the baroreflexes to maintain RNA at elevated blood pressures. The results support our model that the Tc mode reflects a fundamental periodicity of central origin and the Tb mode a periodicity of cardiac related RNA, which is produced by the opening and closing of gate operators to the fundamental rhythm.